                                                (let [scroller (.. e -target -scroll_handler)]
                                                  (when (or (not scroller) (.isStopped scroller))
                                                    (put! controls-ch [:container-parent-scroll]))))
-                                  :scroll "handle_browser_scroll"
-                                  :window-resize "realign_container_viewport"
-                                  :resize-sensor "height_changed"
                                   :class (str "selected_" current-container-id)}
            (for [container containers]
              (om/build container-view
                        {:container container
-                        :non-parallel-actions non-parallel-actions}))]])))))
+                        :non-parallel-actions non-parallel-actions}
+                       {:opts {:uses-parallelism? (< 1 (count containers))}}))]])))))

                     (when (:truncated action)
                       [:span.truncated "(this output has been truncated)"])]])])]]]]])))))

(defn container-view [{:keys [container non-parallel-actions]} owner]
  (reify
    om/IRender
    (render [_]

        (html
         [:div.container-view {:style {:left (str (* 100 (:index container)) "%")}
                               :id (str "container_" (:index container))}
          (om/build-all action actions {:key :step
                                        :opts opts})])))))

(defn mount-browser-resize
  "Handles scrolling the container on the build page to the correct position when
